Vacuum-gage.



I. LANGMUIR' VACUUM GAGE.

APPLICATION FILED NAILS, 1913.

1,126,233. Patented Jan. 26, 1915.

Witnesseslnven tor HisAttorhey.

UNITED STATES PATENT enrich.

mvrnelanemnm, or scnnnncmny, NEW roan, assrenon, '10 GENERAL ELECTRICcomany, A conronarron or NEW YORK.

vacuole-seen.

To all whom it may concern:

- Be it known that I, IRVING LANGMUIR, a

citizen of the United States, residing at Schenectady, in the county ofSchenectady and State of New York, have invented certain new and usefulImprovements in Vacuum-Gages, of which the following is a specification.

The present invention relates to the measurement of high vacua.

The term vacuum as commonly used denotes a rarefied atmosphere which hasan appreciable and measurable pressure. As the apparatus for exhaustinggases has become improved the degree of rarefaction has steadilyapproached the theoretically perfeet vacuum making the measurements ofthe minute residual gas pressures increasingly difficult. The wellknownMcLeod gage will measure a pressure of about 0.01 of a micron, in .otherwords, a pressure 0.00001 of a millimeter of mercury. It does not takeaccount of vapors, such as the vapor of mercury, water, or oil. Recentimprovements in evacuating apparatus have made possible the attainmentof still lower pressures. In accordance with my invention these very lowpressures are measured by observing the drag, or torque exerted upon asuspended body by the impact of the residual gas molecules when set intomotion at a predetermined rate. This method is carried out in appartusin which a disk, or other bodyof extended surface, is rotated at a givenspeed in proximity to another body in the evacuated space.

In the accompanying drawings, Figure 1 is a vertical section of thevacuum meter or gage, Figs. 2 and 3 are diagrams of a preferred form ofelectrical driving device, and Fig. at illustrates diagrammatically anindicating device.

In Fig. 1 the receptacle 1 consists in part at least of transparentmaterial, as glass, quartz or the like, connected to the chamber, orsystem, in which the vacuum is to be measured through a tube 2. In thisreceptacle is mounted a motor armature 3 which may consist of a body ofmagnetic material having opposite poles as indicated which revolves insynchronism with an exterior field. It is mounted on a shaft 4 which ispivoted upon a jewel bearing 5. A light disk 6 consisting preferably ofaluminum, is also mounted upon the shaft 4. The shaft is Specificationof Letters Patent.

accurately centered and supported by a frame work 7, the shaftpreferably passing through a jewel 8. ,A second disk 9, preferably ofnonconducting material, as mica, is supported in close proximity to themotor disk 6 by means of a quartz fiber 10, or other suitable torsionalsupport. Upon the stem 11- attached to the disk is mounted a mirror 12.The motor element of the gage is rotated by a revolving magnetic fieldprodueed by the winding 13 which may be provided-with a magnetic core14, although the latter is not absolutely necessary. The winding 13 isin effect the field coil of a synchronous motor, and may be constructedaccordingly. The winding 13 is divided into sections which may besupplied with polyphase alternating current. However, as shown in Figs.2 and 3, they are preferably supplied with opposite pulsations ofcurrent derived from a direct current source such as the generator 24.The conductors 15, 16, 17, 18, 19 and 20 are connected to slip rings,which are connected respectively to sections 15, 16, 17, 18, 19 and 20'of a commutator upon which bear brushes 21 and 22. When the. commutatoris rotated, as by belt 23, the connection from direct-current source 24is progressively transferred from wires 16 and 19, to .17 and 20, to 18and 15, and so on. In this way the field shifts thus rotating insynchronism the member 3. In this manner the motor element may be drivenat any pre- "determined constant speed, and by varying the speed of therotating member the sensitiveness of the gage may be controlled- Greatersensitiveness may be' secured by higher speeds.

The rotation of the disk 6 imparts a torque to the disk 9 proportionalto the pressure of the residual gas and the square root of the molecularweight. This torque is due to the frictional engagement of the disk 6with the gas molecules in the chamber' 1 causing a movement of the gasmolecules which exerts a drag upon the disk 9 twisting it in proportionto the gaseous pressure for any given gas. A torsional support, such asa quartz fiber, exerts a twisting moment or restoring torqueproportional to the angle through which the fiber is twisted. As therotating disk may be revolved at a very high speed very low pressuresmay be measured in this manner with great accuracy and the presence ofvapors of mercury Patented Jan. 2%, 19115. Application filed March a,1913. Serial No. 752,954.

My device maybe used for measuring pressures below about 0.5 m. m. ofmercury, and it is particularly useful for measuring the very lowpressure attainable by such devices as the molecular pump.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. The method of measuring the pressure of the residual gas in anevacuated space which consists in setting the residual gas in motion ata predetermined rate, and determining a force exerted by such gas byvirtue of its motion.

2. A vacuum gage comprising an evacuated gas-tight envelop a rotatablemember mounted therein, means for rotating said member at a constantspeed, a movable body in proximity to but out of contact with saidrotating member, and means for indicating the displacement of saidmovable body effected by the rotation of said member.

3. A vacuum gage comprising a gas-tight chamber, a motor disk mountedtherein, means for rotating said disk at a predetermined rate, a disksuspended in proximity to but out of contact with said motor disk, andmeans for indicating the torque exerted on said suspended disk.

4. A vacuum gage comprising a gas-tight chamber, a rotatable member ofextended surface mounted therein, means for rotating said member, and atorsionally suspended 6. The method of measuring the pressure I of ahighly attenuated gas which consists in mechanically transmitting atorque to a body through the medium of the residual gas and determiningsaid torque by the displacement imparted thereby to said body.

7. A gage for measuring the pressure of a highly attenuated gascomprising an envelop, a rotatable member therein for extended surface amovable indicating member also of extended surface mounted in closeproximity to but out of contact with said rotatable member, means fortransmitting torque to said indicating member through the frictionalengagement of attenuated gas whose pressure is to be measured,

means for opposing the displacement of the indicating member by arestoring torque, and means for indicating the amount of displacement ofthe indicating member.

In witness whereof, I have hereunto set my hand this sixth day of March,1913.

, IRVING LANGMUIR. Witnesses:

BENJAMIN B. HULL, HELEN ORFORD.

It is hereby certified that in Letters Patent No. 1,126,233, grantedJanuary 26, 1915, upon' the application of hiring Langmuir, ofSchenectady, New York, for an improvement in Vacuum-Gages, errors appearin the printecL specification requiring correction as follows: Page 1,line 80, for the reference-numeral 15 read 15'; page 2, line 12, for theword pressure, read essures; same page, line 63, for the word ""for readof; and that the said Letters Patent sh'oul'oi be read with thesecorrections therein that the same mayconform to the record. of the casein the Patent Qfice.

Signed and sealed this 9th dayof February, A. 1D,, 1915,

, [snan] J. 'r. NEWTON,

Acting Uommiesioncv of Patents

